postgres_explain_analyze_json_schema

a JSON schema for postgres ``EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS)` yaml or json.

Methodology

Unfortunately, the schema is hand-maintained.

1. I generated many the output of many EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS, FORMAT YAML) queries in pg_inventory
2. an initial skeleton of the schema was generated with the python genson package using ./scripts/generate_initial_schema.py,
3. guessing which string types have constrained values, (i.e. any key ending in " Type:"), I used ./scripts/collect_enums.sh to generate enumeration values and hand-defined the enumerations
4. I extracted a definition of a Plan object and used it to recursively define itself
5. I transformed the JSON into the primary document, schema.yaml using ./scripts/to_yaml.py
6. I test the definition against the corpus of YAML I have using ./scripts/validate_schema_against_corpus.py.
7. Re-transform schema.yaml into schema.json for easier distribution